The measurement of the concentration of blood components such as hemoglobin and glucose has required the drawing of a blood sample for in vitro analysis. The need to draw blood for analysis is undesirable for several reasons, including discomfort to the patient, the time required of medical personnel to draw and handle the samples, and the potential risk of spread of disease through punctures of the skin. Repeated drawing of blood samples is especially undesirable in infants. Many diabetics must test their blood up to six times a day to monitor their blood glucose levels. It would thus be desirable to be able to obtain fast and reliable estimates of the concentration of blood components in blood, such as hemoglobin and glucose, through a simple and non-invasive technique. Prior efforts have involved an examination of blood in the skin or extremities, such as fingers and ear lobes, or in observable surface blood vessels, but these efforts have had limited practical success due to the presence of tissue components that interfere with accurate reading of only the concentration of blood components.
There are approximately four million newborns in the United States alone each year. About 50% of newborns are clinically jaundiced from elevated bilirubin levels. If the serum bilirubin reaches very high levels during the post-natal period, kernicterus, neural damage resulting from sustained high levels of serum bilirubin, may occur. Frequent monitoring of serum bilirubin is critical to the care of these infants. Of the newborns that have recognizable jaundice during the first 5 days of life, 1.7 million receive at least one blood test for bilirubin. Of those tested, about 700,000 undergo phototherapy treatment; these infants receive an estimated two to three additional blood tests. Presently, blood is drawn through the heel of the neonate, resulting in occasional infections and other complications. Other drawbacks to this process are its high cost and the delay in lab results reaching the physician. Recently introduced non-invasive devices for measuring bilirubin do not provide the accuracy level required to diagnose or treat elevated serum bilirubin levels, rendering them virtually useless in practice.